A study of Carbon and Nitrogen Free New Alloys with Superior Creep Properties More over 700°C
In order to improve the creep strength of the heat resistant steels at elevated temperatures over 700°C, a new attempt has been demonstrated using carbon and nitrogen free Fe-Ni martensitic and austenitic alloys strengthened by Laves phase such as Fe2W and Fe2Mo. It is important that these alloys are independent of any carbides and any carbo-nitrides as strengthening factors. The high temperature creep tests over 700°C exceed 36,000 hours and the test is continued. Creep behavior of alloys is found to be completely different from that of the conventional high-Cr ferritic steels. The alloys exhibit gradual change in the creep rate with strain both in the transient and acceleration creep regions, and give a larger strain for the minimum creep rate. Effect of Cr on the Fe-12Ni-9Co-10W alloys on the creep properties more over 700°C was investigated. It became clear that the value for 100,000 hours was exceeded at 700°C and 100MPa calculated from the Larson-Miller parameter at C=20. And surface appearance of crept specimen was investigated in detail.
S.W. Nam, Y.W. Chang, S.B. Lee and N.J. Kim
S. Muneki et al., "A study of Carbon and Nitrogen Free New Alloys with Superior Creep Properties More over 700°C ", Key Engineering Materials, Vols. 345-346, pp. 593-596, 2007